The long range objective is to utilize isolated nucleoli of the Novikoff ascites tumor and other rat tissues for study of the synthesis and processing of ribosomal RNA and ribosomes in vitro. This will require dissection and recombination of the many components of the system: DNA templates, RNA polymerase, RNA methylase, ribonucleases, ribosomal proteins, etc. The mechanisms of control of these reactions (both natural metabolic regulation and selective inhibition by antimetabolites) and their application to malignant growth are being given special consideration. In previous work, conditions for obtaining synthesis of sibosomal RNA in isolated nucleoli were established. Recent work has shown: 1) the nucleoli contain ribosomal RNA methylases acting on both bases and ribose of the nascent pre-ribosomal RNA, 2) the nucleoli contain a group of transfer RNA methylases, which may be associated with the nucleolar protein synthesizing system, 3) poly (I) and poly (G) inhibit both cytoplasmic and nucleolar tRNA methylases, as well as nucleolar rRNA methylases, relatively selectively for adenine methylases, and 4) poly (I)(C) (shown by others to inhibit growth of certain tumors) has been found to inhibit methylation of tRNA adenine and rRNA ribose in Novikoff cells in vivo. The immediate objectives are to puruse the characterization of the nucleolar methylases of ribosomal RNA and their role in the processing of pre-ribosomal RNA, to search for additional specific inhibitors (both natural and artificial) of RNA methylases, and toestablish the mecanisms of action of those inhibitors, both in vitro and in tumor tissues, as potential chemotherapeutic agents. The addtion of poly U to rRNA in nucleoli and its possible role in polysome function is also under study.